FIG. 35 is a block diagram of a conventional position reading apparatus. First of all, referring to this drawing there will be described operation for detecting a position in the conventional position reading apparatus.
The apparatus has a structure that exciting lines 903 and sense lines 902 are laid orthogonally, and each exciting line 903 is sequentially selected by being coupled to a first scanning circuit 908 in turn and each sense line 902 is sequentially selected by being coupled to a second scanning circuit 909 in turn. As the first scanning circuit 908 is supplied with an exciting signal s906 from an exciting circuit 915, the exciting line selected by this circuit generates an a.c. electromagnetic field. A position pointer 906 includes a resonant circuit (hidden from the Figure) which resonants with a frequency of the exciting signal s906. Therefore, when the position pointer is put on the sense lines, induction signals s901 generate on the sense lines 902 because of the coupling among the exciting lines 903, the position pointer 906 and the sense lines 902. The second scanning circuit 909 selects each of the sense lines sequentially and thereby the induction signal s901 is guided to a signal processing circuit 904 and is converted into an amplitude signal s905. Further, the amplitude signal is inputted into a position detecting circuit 905 and then the position is calculated from a distribution state as to the induction signal s901 at an intersection point of each exciting line and each sense line.
It is necessary to select a plurality of the sense lines in order to obtain the distribution state as to the induction signal s901. In such a conventional position reading apparatus as explained above, calculating the position of one point requires performing selecting operations in matrix in a way that a plurality of the sense lines are selected while each of the exciting lines is selected. For instance, if the five exciting lines and the five sense lines are to be selected respectively, the position of a point is calculated by performing twenty five times of selecting operations in total because the five sense lines are selected whenever one of the exciting lines is selected.
Next, referring to FIGS. 36A and 36B, there will be described an operation for detecting a state of switches and so on provided for the position pointer in the conventional position reading apparatus.
As shown in FIG. 36A, the position pointer 906 has a construction that the position pointer 906 includes a resonant circuit 907 and the resonant circuit 907 is connected in parallel to a switching circuit 913 in which the switch and a second capacitor are connected in series. Then, when the switch is pushed, a resonance frequency slightly changes.
Therefore, as shown in FIG. 36B, a phase of the induction signal s901 is slightly different between when the switch is on and when the switch is off. A state of the switching circuit 913 can be detected by detecting this phase change .phi..
Further when a number of switches are provided on the position pointer and many status are required or when the condition settings are required to extend in such the conventional position reading apparatus, for example, by providing a pressure detecting function with the position pointer, such requirements are realized in a manner mentioned below. Detection accuracy is ensured by providing the main body with a detecting circuit capable of detecting a slight change in phase accurately and also stably. At the same time, in the process of manufacturing the position pointer, the resonance frequency of the resonant circuit is accurately adjusted and parts of high stability are used so that even after the adjustment the detection accuracy is highly stable against environmental changes such as temperature change and time passage.
In the conventional position reading apparatus, it is necessary that an a.c. electromagnetic field of a predetermined frequency is always generated from the exciting lines. Generation of the a.c. electromagnetic field is required all the time for detecting that the position pointer is placed, even if the position pointer does not exist in the vicinity of the sense liens, that is, even when position detection is not necessary. Therefore, an exclusive exciting circuit is necessary for generating the a.c. electromagnetic field.
Further, there is a problem that a position can not be calculated at high speed because the lines required to be selected in matrix as explained above in order to calculate the position of a point.
Moreover, as shown in FIG. 37, in the sense lines laid near a periphery of a body of a detecting device, a direct coupling between the exciting line and the sense line is generated in portions A and B. As a result, the induction signal is generated even if the position pointer does not exist. This fact means that induction signal components which are not dependent on the position pointed by the position pointer are added to the sense lines near the periphery of the body of the detecting device, which cause a problem that accuracy of position detection deteriorates around the periphery.
Detecting a state of the position pointer, for example, a state of switches, uses a phase difference resulting from a slight difference between the frequency of the exciting signal and the resonance frequency of the resonant circuit, therefore the switching circuit in the position pointer and a phase detecting circuit in the body of the detecting device require very precise frequency setting. Further, the phase difference is required to be generated in each switching circuit in order to detect states of a plurality of the switches, but a range in which phase difference are generated is limited. Therefore, the conventional position reading apparatus can not be constructed so as to be capable of detecting the states of so many switches. Though sixteen or more switches are demanded in the market, it can not be realized in the conventional apparatus.
A first object of the present invention is to realize a wireless position reading apparatus which does not require the body of the detecting device and the position pointer to be connected with a signal wire and in which a circuit can be more simplified by eliminating the exciting circuit compared with the conventional apparatus.
A second object of the present invention is to realize the position reading apparatus capable of calculating a position with high speed in addition to the above first object.
A third object of the present invention is to realize the position reading apparatus in which a peripheral accuracy does not deteriorate in addition to the above first and the second objects.
Further, a fourth object of the present invention is to realize the position reading apparatus which can detect a status of a position pointer with a circuit that does not particularly require a precise setting and which can easily detect a plurality of statuses in addition to the above the first to the third objects.
Furthermore, a fifth object of the present invention is to provide, by applying the invention to a key board apparatus, a key board apparatus in which a key board operates without power supply and transfers the switch information without contact and further which does not require a space for the large connector in the host system.